Now doesn't that PCB look nice? You will be amazed at how much gunk comes off a dirty board. This photograph shows only a small portion of the dirty cotton buds.
The small glass dish on the upper left of this photograph is used to hold the isopropanol. The Noctua fan is blowing from right to left, so the fumes arising from the dish of isopropanol are not driven into my face as I work.
Isopropanol is not the same as ethanol that you can drink. It is many times more toxic. Take this warning seriously.